Triangle Seminars

Abstract:
Description:
Courant algebroids provide a natural framework for working with the low energy limits of string theory. In particular, they are well suited for the study of Poisson-Lie T-duality, which is a generalization of the usual T-duality. We will discuss how to see bosonic fields of type II supergravity as structures on Courant algebroids (generalized metrics, spinors and divergence operators). We will then construct appropriate curvature tensors and use them to prove the compatibility of Poisson-Lie T-duality and the equations of motion of supergravity. The framework also allows us to use algebraic methods to search for new (non-isometric) string backgrounds. This is a joint work with Pavol Å evera.

[please email a.held@imperial.ac.uk for zoom-link]

Abstract:

I will summarise my research interests and recent work, which is mainly related to the problems of field and gravity theories with extended symmetries. Such systems are the higher-spin and coloured gravity theories, theories of non-abelian chiral p-forms or partially-massless fields (satisfactory interacting theories of which are still missing).

[please email a.held@imperial.ac.uk for zoom-link]

Abstract:
A simple probe of chaos and operator growth in many-body quantum systems is the thermal out of time ordered (OTO) four point function. In a large class of local systems, the effects of chaos in this correlator build up exponentially fast inside a so called butterfly cone. I will discuss universal features of the spatiotemporal structure of this exponential growth in large N systems. In particular I will argue that there can be a smaller, “scramblon” cone inside the butterfly cone. Outside the scramblon cone, the growth of the OTO four point function is completely universal and saturates a chaos bound. I will explain the connection to conformal Regge theory, where crossing the scramblon cone is related to an exchange of dominance between the pomeron and the stress tensor. Finally, I will discuss a connection between chaos and energy transport, called the pole skipping phenomenon, which is a subtle effect in the thermal energy density retarded two point function at a special point in the complex frequency and momentum planes. I will present an improved understanding of this connection and test it in the large q limit of an SYK chain, where I determine both the Lyapunov growth of the OTO correlator and the energy density two point function exactly as a function of the coupling, interpolating between weekly coupled and maximally chaotic behaviour.
[For the Zoom link, please email to: alejandro.cabo_bizet@kcl.ac.uk ]

Abstract:
In this talk I give an overview of the Yangian symmetry of Feynman integrals. After reviewing the connection between AdS/CFT integrability and the Yangian symmetry of massless Feynman graphs, I discuss the idea to bootstrap Feynman integrals based on the Yangian constraints. Then I show that also in the massive case large classes of Feynman integrals are constrained by a Yangian extension of dual conformal symmetry. When translated to momentum space, this leads to a novel massive generalization of ordinary conformal symmetry. Finally, I argue that these features of massive Feynman integrals can be understood as the integrability of planar scattering amplitudes in a massive version of the so-called fishnet theory, which is obtained as a double-scaling limit of N=4 super Yang-Mills theory on the Coulomb branch.
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